One of the cardinal rules of horse racing is that betting on favorites is fun — who doesn’t like having a winning ticket? — but it’s the quickest way to go broke. Except, that is, in the most famous race in America.

The Kentucky Derby should be nearly impossible to handicap. The horses, at just 3 years old, don’t have much experience and are still maturing. Many of them have never run this distance before, or run at Churchill Downs. And even if a handicapper can sift through all that uncertainty and use a combination of past performances and pedigree to identify the best contenders, it can all become irrelevant thanks to the abnormally large Derby field — with as many as 20 horses creating gridlock and chaos, results ought to be utterly unpredictable.

That’s what makes the last several years of the Kentucky Derby so strange: It is, seemingly, getting more predictable. For four straight years, the favorite has come out on top. It began with Orb in 2013, then continued with California Chrome, American Pharoah and Nyquist.

In total, 16 favorites have won the Kentucky Derby in the last 50 years.1 And that has produced a compelling betting strategy: Forget all the wonky handicapping. Over the last half-century, placing a $2 bet (the smallest bet you can make on a single horse in the Derby these days) on the favorite each year would have netted you $107.80 on a $100 investment — a 7.8 percent profit. But in just the last 20 years, returns on that same strategy would be much better: 74 percent.

Now the question has become: Is the recent rash of victorious favorites a coincidence? Or a sign of something bigger?

Before these last four years, the Kentucky Derby had for decades been known for its unpredictability. Between 1980 and 1999, not a single favorite won. Before 2013, it had been four years since a favorite wore the roses.

There are two rational explanations for this trend. The first is chance. These horses, after all, are the favorites for a reason. And this kind of streak is not unprecedented — favorites won four straight years from 1972-1975, too.

But there’s another rationale that would indicate that this is more than a fluke. It explains why the Kentucky Derby is getting chalkier and why the mega-longshot winners we once saw regularly in this race might become increasingly rare.

When Orb won the Derby in 2013, that wasn’t just any year. It was the first year that horses qualified for this first leg of the Triple Crown under a newly implemented points system. This “Road to the Kentucky Derby” awards points to the top four finishers in a select group of races. The top 20 get to run in the Derby.

What’s more important than the point system is the mechanism it replaced. Before 2013, horses qualified for the Derby based on their winnings in graded stakes races.

This created chaos in the Derby. In some instances, horses that were elite in sprints — races shorter than a mile, which are excluded from the new qualifying system — could crowd the Derby, a route run at 1¼ miles. In other instances, horses that weren’t good enough made it in anyway. But these horses didn’t just fade down the stretch into irrelevance. They regularly introduced anarchy, transforming the subtle mechanics of a race in a way that allowed longshots to thrive.

There’s no more illustrative example than the 2005 Derby, when 50-1 longshot Giacomo stunned the world. Giacomo’s best friend in that race was a 71-1 longshot named Spanish Chestnut, which led for the first three-quarters of a mile. In the last two races Spanish Chestnut ran before the Derby, it finished sixth twice. In other words, it didn’t belong. But during those first six furlongs, Spanish Chestnut set the second-fastest pace in Derby history.

Predictably, Spanish Chestnut couldn’t sustain such a hot pace, ultimately fading and finishing 16th. But while this longshot was in the lead, other horses got sucked into running that fast and wound up tiring, too. The favorite that day, Bellamy Road, was close by, in fifth place, when Spanish Chestnut started to slow.

At that same distance, three-quarters of a mile, Giacomo was in 18th place out of 20 and trailed by 14¾ lengths, the farthest behind of any eventual Derby winner in more than a quarter-century. But when Spanish Chestnut — and every horse that tried to keep up with Spanish Chestnut — tired, Giacomo had enough gas left in the tank to pass 17 other horses.

The new points system is better at weeding out the Spanish Chestnuts. That means longshots like Giacomo are even less likely to encounter the volatile circumstances that enable them to win.

The strategy of betting the favorites for 50 years would also pay off in the Preakness Stakes, the Triple Crown’s second leg. In fact, in the long run you’d make more than you would on the Derby — the Preakness has offered returns of 11.4 percent. But in any single year, betting on a favorite in the Preakness can be less attractive: When American Pharoah and California Chrome won, for example, they went off at odds shorter than 1-1, meaning that if you cashed in on a $2 bet, your winnings would likely be counted out using more quarters than dollar bills. Essentially, it requires risking a lot of money just to win enough to pay for a celebratory cigar.

On the other hand, because the Derby is so uncertain, favorites can be had at good value. This year’s morning-line favorite, Classic Empire, is priced at 4-1. That would offer better returns any Preakness favorite in the last half-century.

At the same time, the biggest sucker’s move is betting a favorite in the Belmont Stakes, which at 1½ miles is longer than almost any other race these horses will ever run. In other words, nobody knows how the horses will handle the distance. What’s worse, the favorite will often be racing for the third time in seven weeks, which can leave a horse worn down. A bet on the favorite in the Belmont in the last 50 years would have cost you 38.7 percent of the money you staked. There’s a reason we went nearly 40 years without a Triple Crown winner before American Pharoah came along.

All of this means that the best betting strategy for this year’s Derby may also be the dumbest one: Bet on Classic Empire.

Footnotes

Including Forward Pass, the favorite in the 1968 Kentucky Derby who initially finished second but was awarded the win after first-place finisher Dancer’s Image was disqualified for failing a drug test. Bets on Dancer’s Image may have been paid out before the horse was disqualified, but for the purposes of this thought experiment, we’re counting things as if Forward Pass won the usual way.